Method for flame bonding by use of high velocity,high temperature direct flame

ABSTRACT

A METHOD AND APPARATUS FOR OBTAINING RAPID BONDING OF THERMOPLASTIC MATERIALS TO THEMSELVES OR OTHER SIMILAR OR DIFFERENT MATERIALS BY THE USE IOF A HIGH VELOCITY, HIGH TEMPERATURE DIRECT FLAME IN COMBINATION WITH PRESSURE. THE METHOD IS SUFFICIENTLY RAPID SO THAT THE PROPERTIES OF THE MATERIALS ARE NOT SUBSTANTIALLY DETRIMENTALLY AFFECTED. THIN LAMINATES OF HIGHLY ORIENTED MATERIALS CAN BE BONDED WITHOUT LOSS OF STRENGTH CHARACTERISTICS.

Jan. 1, 1974 3,783,062

W. N. MARTIN METHOD FOR FLAME BANDING BY USE OF HIGHVELOCITY, HIGHTEMPERATURE DIRECT FLAME Filed Jan. 27, 1972 2 Sheets-Sheet l Jan.1,.1974 w N MART|N 3,783,062

METHOD FOR FLAME BANDfNG BY USE OF HIGH VELOCITY, HIGH TEMPERATUREDIRECT FLAME Filed Jan. 27, 1972 I 2 Sheets-Sheet 2 United States PatentC US Cl. 156--82 9 Claims ABSTRACT OF THE DISCLOSURE A method andapparatus for obtaining rapid bonding of thermoplastic materials tothemselves or other similar or different materials by the use of a highvelocity, high temperature direct flame in combination with pressure.The method is sufiiciently rapid so that the properties of the materialsare not substantially detrimentally affected. Thin laminates of highlyoriented materials can be bonded without loss of strengthcharacteristics.

This invention relates, in one aspect, to bonded or laminated materials;in a' further aspect, this invention relates to an improved method bywhich two or more layers of materials may be laminated together by meansof flame bonding; and in a still further aspect, to an apparatus forcarrying out the method to produce bonded or laminated materials. q

More particularly, in accordance with the method of this invention,there is provided a novel method of bonding or laminating two or morelayers of materials together to form an improved bonded laminate, byemploying a high velocity, high. temperature flame in combination withpressure in such amanner that the desirable properties of the layers ofthe materials being bonded together are not substantially detrimentally.affected by the flamebonding conditions.

PRIOR ART Flame treatment of thermoplastic surfaces, to render the samesusceptible 'to bonding to one for more layers of other materials, iswell known in this art. The flame treatment, using a combustible gaseousagent, has been used to treat such materials as thermoplastic surfaceswhereby such surfaces are susceptible to adhering to various types ofmaterials-for example, coating or printing materials, etc.

One prior artmethod inparticular, involves impinging a jet of hot airor. gas at a velocity of from 4,000 to 10,000 feet per minute, whileemploying temperatures of -600 to 1,000 F., against the surface of athermoplastic film to render it bondable to another film. The two filmsare then pressed "together to form a laminate. In this'prior artteaching, higher velocities'are not recommended. In copendingapplication, Ser. No. 819,752 filed Apr. 28, 1969, now abandoned thereis disclosed amethod of bonding two layers of materials together,wherein one such layer is thermoplastic, by applying'a flame directly tothesurface of the thermoplastic material immediately prior to 3,7832%2Patented Jan. I, 1974 pressing the layers together. In this technique,and in general of the prior art methods, flame bonding results in thedeleterious alteration of the bulk characteristics of the material beingtreated, so that upon obtaining a bonded material or laminate, theproperties of the combined materials are substantially different fromthose of the individual layers prior to bonding treatment. In thisrespect, this has been found to be particularly the case with very thinfilms and/or webs. Likewise, in the case of highly oriented materials, afurther disadvantage is that the strength characteristics of thematerial are reduced, which in some cases, will make the resultingbonded laminate unsuitable for certain uses.

At the present time, flame bonding techniques have not found commercialusage to any extent, but rather, they have been replaced by otherbonding techniques due to the above disadvantages. A further reason forother bonding techniques substantially replacing flame bonding is thatuniform, controlled results cannot normally be obtained compared toother techniques. This will be evident from examination of bondedmaterials or laminates produced by conventional flame treatingtechniques wherein, e.g. one thermoplastic film is bonded to itself orto nonthermoplastic materials such as paper, metal materials e.g. foils,etc. as tests will show that variations in the degree of bonding areprobably considered to be caused by a non-uniform distribution of flametemperatures.

With this invention, applicant has developed a novel method of flamebonding various types of materials to themselves, or to other materials,which method overcomes the disadvantages of the prior art and provides aresulting bonded material or laminate substantially free from thedisadvantages of prior art bonded materials or laminates. Still further,the method of this invention does not detrimentally affect theproperties of the materials being bonded to any extent, as compared toprior art procedures, and the resulting bonded laminate or product hassubstantially the same properties as the individual materials formingthe product. Thus, the resulting product does not possess a loss ofstrength characteristics c0mpared to products which were produced byprior art techniques.

In accordance with the method aspect of this invention, there isprovided an improvement in a method of bonding wherein there is provideda supply of such bondable material, said supply including at least onebondable thermoplastic material, heating the surface of said material byapplying, in direct contact therewith, a high velocity gaseous flame,said heating being applied to such surface to render the surfacesubstantially uniformly heated in a substantially continuous paththereon, said flame having a flame velocity of above 10,000 feet perminute and a temperature above 1,000 E, subsequently causing the heatedsurface to be brought into juxtaposition with a further surface andpressing said heated surface and said further surface to form asubstantially uniformly bonded laminate.

In accordance with a further aspect of this invention, there is provideda product which in brief summary, includes at least one layer of athermoplastic material substantially uniformly bonded to a further layerwithout the use of adhesives, the thermoplastic layer having been heatedwith a gaseous high velocity flame having a velocity greater than 10,000feet per minute and a temperature of higher than 1,000 F. and pressedagainst said further layer, the bonded material having the property ofsubstantially no reduction in bulk characteristics compared to thematerials individually forming the bonded material.

In carrying out the process of the present invention, the bondingvelocity (denoting the velocity at which the heated surfaces to bebonded together, are brought into juxtaposition) will depend on severalfactors, including the nature and type of surface and material beingbonded, as well as other parameters defined hereinafter. For any givenset of conditions or parameters, the bonding velocity should desirablybe maintained as high as possible commensurate with achieving adequatebonding. Where adequate speed controls are available, it will bepossible to control the degree of bonding and bulk property effects byvarying the bonding speed. Thus, for example, by increasing the bondingvelocity from a rate of 125 feet per minute to 200 feet per minute, thebulk tensile of a Woven laminate increased from 34 p.l.i. to 82 p.l.i.,and the bond strength (peel) decreased from 7 p.l.i. to p.l.i. (as shownin the accompanying examples).

Desirably, the flame velocity (and depending on the application) ismaintained as high as possible, having regard to technical feasibilitiesof the equipment being used to carry out the process. In the prior art,recommended flame velocities were generally much lower than 10,000 feetper minute (f.p.m.) to avoid such problems as surface rippling. Incontrast, it has been found by the applicant that very high rates ofheat transfer can be effected by very high flame velocities and whencombined with the proper bonding velocity, the surface depth to whichmelting will occur can be restricted to microscopic dimensions therebyavoiding any bulk surface defects (in addition to avoiding other bulkeffects mentioned above). For these and other reasons, the process ofthe present invention utilizes flame velocities above 10,000 f.p.m., anddesirably within the range of from 12,000 to about 40,000 (or higher)f.p.m. This range of flame velocities has been found very effective toproduce satisfactorily bonded products, when using a propane-air gaseousflame mixture. In this respect, as used in this specification, the termflame velocity in its proper context refers to the velocity of a flamejet as it leaves the burner exit.

In carrying out applicants process, and as briefly outlined above, it ismost desirable that all of the inter-related factors of the process areso chosen so as to obtain or utilize the highest intensity of eachfactor or parameter, to ensure and obtain the best possible commercialbenefits (by, for example, maintaining the time element for treatment toa minimum commensurate with obtaining a desired bonding withoutsubstantial loss of bulk properties of the material being treated). Inthis respect, as the time element is dependent on bonding velocity, sothe desired flame temperature will depend to a large extent on bondingvelocity and accordingly, since the highest possible bonding velocitiesare preferred, the highest possible temperatures are likewise mostpreferred in practicing the present invention. Thus, according to apreferred feature, and having due regard to economic combustiblecommercially available gases, temperatures above 2,000 F. are preferredand generally in the order of from 2,4002,800 F. which have been foundto be particularly effective using a gaseous propane-air mixture.However, temperatures above 1,000 F. have also been found effective forsome products.

Within the scope of the present invention, and in general terms, mostsatisfactory results have been obtained when utilizing a flamepositioned generally as close as possible to the surface(s) to be heatedand bonded; however, as in the case of flame temperature, the flamelocation can also be varied depending on the bonding velocity. Stillfurther, depending on the use of the end products and the nature of thesurface(s) being heated, it may be desirable in certain circumstances tobring certain parts of the flame into direct contact with the surface(s)being treated. Thus, for example, in certain situations, it is desirableto bring an oxidizing flame, rather than the reducing portion of theflame, into contact with the bonding surface( s), or vice versa.

In general, the flame should also be as close as possible to the bondingpointi.e. as close as possible to the point at which the heatedsurface(s) are brought into juxtaposition with each other (or in otherwords, the bonding nip). To some extent, as will be obvious to thoseskilled in the art, the degree to which the bonding flame can be broughtinto proximity with the bonding nip will be dependent on the physicalgeometry of the bonding areafor example, on the size of the nip rollsused in bonding, and on the uniformity of the bonding (i.e. uniformityof temperature/heat transfer in the flame-surface contact area). Thus,for instance, improved bonding uniformity may require spacing the flameaway from the bonding nip to allow additional time for betterdistribution of the heat/temperature prior to actual bonding. Thus,control/selection of flame temperature can also be effected if desired,by controlling the location of the flame.

In situations where it is not possible to locate the hottest part of theflame adjacent the nip due to physical limitation-s, smaller nip rollsmay be employed in advance of the large nip rolls, of a laminatingapparatus. In a further embodiment, when the laminating apparatusemploys large nip rolls, they may be spaced a substantial distance fromthe small nip rolls with the result that the same roll arrangement canbe used for other purposes, as described hereinafter in greater detail.Where dual functioning rollers are not required, and where large andsmall pairs of such rollers are employed, the larger pair shouldpreferably be as close as possible to the smaller nip rolls; althoughfor different applications, the distance between the nips may influencebonding strength and accordingly, an optimum distance may be selectedfor any given application. Applicant has found it desirable, for anygiven set of conditions established by a particular bonding apparatus,and for production of a wide variety of products, it is desirable thatthe (1) distance between the large and small nip rolls, (2) the diameterof such rolls, (3) the distance between the small nip rolls (i.e. thegap) and (4) the nip pressure should all be adjustable or variable topermit optimum values for any given product to be selected as desired.

In situations where the accumulation of combustion products from theflame can create difliculties, e.g. when using open nip rolls (prior tothe main combining nip rolls) in combination with long bonding widths,part of all of the flame stream may be arranged to flow counter to thedirection in which the materials to be bonded are moving. That is,instead of the flame being aimed directly at the center of the nip, itmay be set at an agle which will allow the combustion products to escapemore easily. In such cases, it may also be desirable to use more thanone flame. I

Still further, it has been found that in addition to obtaining a highrate of heat transfer desirably as high as possible) between the flameand the surface(s) to be heated, by the high flame temperature and flamevelocity, a further essential factor has been determined to be themaintenance of a uniform distribution of these parameters to ensureuniform bonding of the materials. Where the width of the flame-surfacecontact area can be covered by or stretched across the width of oneburner, the problem of maintaining uniform distribution of temperatureand heat transfer is substantially less than where one or more flamesources or burnersare required. Unfortunately, commercially availablehigh velocity burners with of the material to be treated). In thisrespect, a study of the'temperature profile has shown that where morethan one burner is used, and such burners were mounted in a side-to-siderelationship (as close as possible) it was found that low temperaturezones existed in the inbetween areas of adjacent burners. To overcomethis problem, it is within the scope of this invention that one ofseveral alternatives may be employed. Thus, for example, burners havinga generally rectangular shaped gaseous discharge opening may be mountedin a staggered relationship so that the high temperature zones of eachburner very slightly overlap each other. In such an arrangement, apreferred embodiment includes the staggering of adjacent burners at anangle to each other, to obtain a substantially continuous and uniformtemperature line across the width of the material being heated. Forflexibility in operating such burners, it is desirable that they beadjustably mounted to permit a variety of applications. In general,staggering adjacent burners at an angle of between about 55 to about 60was found to give a satisfactory and uniform high temperature line closeto the opening of the burners. It will be understood, however, that thisangle will vary depending on several factors, including the size of thenip rolls and accordingly, adjustments may be made as desired.

In an alternate embodiment of the above, there may also be used burningmeans which include a generally circular shaped gaseous dischargeopening, capable of creating a generally circular flame. By utilizingsuch means, there may be produced a round flame which fans out, therebyincreasing the effective heating area compared to the actual size of thedischarge opening in the burner means. Thus, a plurality of such meanscould be employed, again in a generally staggered relationship, toprovide a heating zone of a desired width.

In a still further alternative for securing a more uniform temperatureand heat transfer distribution, there may also be employed a bonding orlaminating apparatus which includes an open nip in advance of thelaminating or bonding nip rolls per se, to provide an area for the hotgases of the flame to mix, spread out and level out the temperatureprofile. Studies by the applicant have shown that for greatest bondingstrength in certain applications the nip opening or gap should not begreater than approximately one-half the height of the blast opening(i.e. the thickness of the flame). Thus, for example, utilizing a blastopening having a height of approximately 125 mils, a nip opening ofapproximately 50 mils has been found to provide optimum bond strengthfor certain applications. While not wishing tobe limited to any theory,it appears that when the nip opening. is smaller than the flamethickness, it allows a portion of the flame to impinge on the surface ofthe material beirig heated at an angle(s) which will break/disturb thetravelling boundary layer of gas adjacent the surface of the materialbeing heated, and thereby improve the rate of heat transfer. Thisembodiment can be used to advantage with the above described burnerarrangements and methods, or in the alternative, by utilizing thepreviously described procedures with the burners located in aside-by-side relationship.

For use in the present invention, any suitable combustible gaseoussubstance may be employed to provide the heating flame, which gaseoussubstance is capable of reacting in situ, to produce the requisite hightemperatures employed by applicants process. Preferably, the gaseoussubstance is a gaseous mixture of a hydrocarbon fuel and a gascontaining oxygen, whereupon, on combustion, there may be produced watervapor as one of the by-products. In this respect, it has been found thatwater and/or water vapor can play a significant role in the bonding ofthemoplastic surfaces. For example, for certain laminates it has beenfound that the strength of the bond increases during storage. While thisis not fully understood, it is apparent that the role of the water Willvary with the application and the nature of the materials involved. Incertain instances, to obtain optimum bonding, it may be desirable to addwater vapor to the combustible gaseous material or to the combustionproductsby, for example, injecting steam into the flame. Specific typesof gaseous combustible materials include, e.g., propane and and,hydrogen and oxygen or air, acetylene and oxygen or air, etc. Naturally,as will be evident, the gaseous combustible material should be chosen soas to produce the highest possible temperatures within the mostreasonable cost factor, for commercial purposes.

In carrying out the process of this invention, the heated material maybe bonded together in a suitable apparatus; the bonding pressure chosendepending on several factors including the different types of material,the width and/ or length of the nip roll or like component, etc. Ingeneral terms, higher pressures mechanically required generally largerroll diameters and as mentioned above, larger diameters can interferewith optimum location of the flame for heating purposes. Thus, whilehigher nip pressures might yield slightly higher bonding strength, acompromise normally has to be employed with the other determiningfactors of the process, including economics. In this respect, it hasbeen found, as evident from the following examples, that increased peelstrength can be obtained by utilizing increased nip pressures on smallnip rolls, while maintaining a constant pressure on large nip rolls.Thus, for any given type of material, and other factors as will beevident from the teachings of this disclosure, suitable optimumpressures may be chosen for either or both the large and small niprolls.

As briefly outlined hereinbefore, the apparatus employed to bond orlaminate two or more materials together may be any suitable apparatusfor this purpose. Such apparatus is well known to those skilled in theart of bonding per se, and to this end, at least one pair of opposed niprolls are employed; preferably such opposed nip rolls are adjustablymounted to permit varying degrees of pressure to be exertedtherebetween. Further any suitable means may be employed for feeding thematerial into and through the laminating apparatus.

The process of the present invention may be employed to heat one or morelayers of flame heatable materials, which on subsequent bonding with oneor more additional layers, of the same or diflerent material, is capableof forming a laminate. To this end, suitable materials for use in thepresent invention includue various types of thermoplastic filmmaterials, typical examples of which include polyethylene, polypropylene(of low, medium or high densities in either case), polyvinylchloride,etc. In general, the type of material utilized in the process of thisinvention will depend on the desired end use of such material. Inheating at least one layer of such materials, the resulting heatedmaterial may be bonded to any desired substrateagain, the choice andnature of the substrate will depend on the end use desired. To this end,typically the substrate may be paper, other thermoplastic films of thesame or of a different nature, scrim, non-woven and Woven materials,etc. Still further, if desired, and inasmuch as the products generallyused in the process of the present invention have a pair of opposedmajor surfaces, both surfaces may be heated and subsequently bonded tothe same or dilferent types of substrates on both of said opposed majorsurfaces. In this respect, the process of this application may beemployed as the bonding technique to produce laminates disclosed andclaimed in copending applications Ser. No. 93,646 filed Nov. 30, 1970.

The process of the present application lends itself to production of awide variety and different type of laminates, of varying sizes, shapesand nature. Without being limiting, and by way of example, sheetmaterial may be heated and subsequently bonded to itself to form a tubeor flattened lay-flat tubing; heated material may be subsequentlylaminated to form various types of commercial or consumer products suchas bags, etc.

Having thus generally described the invention, reference will now bemade to preferred embodiments thereof, taken in conjunction with theaccompanying drawings in which;

FIG. 1 is a schematic side elevational view showing certain componentsof the apparatus used to produce the bonded material and carry out themethod of the present invention;

FIG. 2 is a schematic side elevational view of an alternate embodimentto FIG. 1;

FIG. 3 is a perspective view showing burner components used in theapparatus of the present invention;

FIG. 4 is a side elevational view of the burner units of FIG. 3;

FIG. 5 is a side elevational view of alternate burner units for use withthe apparatus of the present invention;

FIG. 6 is a front elevational view of alternate burner units for usewith the apparatus of the present invention;

FIG. 7 is a schematic side elevational view of a general apparatussuitable for use in carrying out the present invention; and

FIG. 8 is a view similar to that of FIG. 7 showing an alternateembodiment.

Referring initially to FIG. 1, reference numerals 10 and 12, asdescribed hereinafter in greater detail. or the like material, assupplied from sources thereof indicated by reference numerals 14 and 16respectively. Reference numerals 18 and 20 denote rotatable guiderollers used to convey the film layers 10 and 12 respectively to thesite of use.

In general terms, the apparatus of FIG. 1 includes a pair of spacedapart rotatable nip rollers indicated by reference numerals 22 and 24,rotating about central axes 26. Suitable means are provided for rotatingrollers 22 and 24 (not shown). The diameters of the respective niprollers 22 and 24 are relatively small, to permit the highesttemperature point, of the hottest commercialy available combustiblematerial forming the flame, to impinge on the surface of the layers ofthermoplastic material 10 and 12, as described hereinafter in greateddetail.

The apparatus also includes one or more burners indicated by referencenumeral 28, mounted by suitable means (not shown) and connected to asource of combustible gaseous material (not shown). As just mentioned,preferably the combustible material is of a type which is of arelatively low cost, commensurate with providing very hot flame, asshown in dotted lines in FIG. 1 and indicated by reference numeral 30.

Following the flame heating operation, as described hereinafter, thelayers of thermoplastic material 10 and 12 pass between the rotatableopposed nip rollers-22 and 24, where they are bonded or laminatedtogether to form a laminate 32, which laminate 32 retains substantiallyall of the strength characteristics of the individual layers 10 and 12and is substantially free from bulk distortion as compared toconventional prior art products. In this respect, the nip rollers 22 and24 are mounted on suitable frame means (not shown) and are desirablyadjustably spring loaded to exert a varying degree of presure, dependingon the type of materials being laminated. Normally, the pressure exertedby the nip rolls on the layers 10 and 12, to form the laminate 32, isadjusted to provide an optimum bond commensurate with obtaining uniformproperties in the resulting laminate. In this respect, nip rollers 22and 24 may be provided with internal cooling means to maintain thetemperatures of the respective rollers at a desired degree and avoidheat build-up.

Referring now to FIG. 2 illustrating an alternate em: bodiment to thatof FIG. 1, the same components designated by reference numerals in FIG.1 are designated by the same reference numerals in FIG. 2, except thatthe components in FIG. 2 include a prime designation. Thus, in FIG. 2,the arrangement of burners and flames illustrated may be employed so asto more easily vent the combustion products of the flame (away from thenip).

In this case, the burners indicated by reference numerals 29 and 31 areseparately directed each to treat one of the webs or layers of materials14' and 16'. Thus, the flames 30' impinge on separate layers 14' and 16'from the different burners 29 and 31.

Referring now to FIGS. 3 and 4, there is illustrated a type of burnerarrangement which may be employed with the apparatus described in FIG.1, to carry out the process of the present invention. More specifically,in FIGS. 3 and 4 there are illustrated three burner units of a generallysimilar configuration, which are rectangulartongue burners. Thus, eachburner indicated generally by reference numeral 40 includes a generallyelongated rectangular aperture 42 discharging combustible gaseousmaterial from a supply thereof (not shown). Each burner 40 is mounted tosupporting means 44, which may be connected by suitable means to theframe of the apparatus. As illustrated in FIG. 4, the burners 40 aremounted in a generally staggered relationship whereby the apertures 42just meet or slightly overlap each other. The triangularly shapedconfiguration of the bunrers, as will be seen from FIG. 3, are generallyinclined slightly at an angle to each other--in the order of from 55 to60. Thus, opposed staggered rows of such burners may be employed, thewidth of the total burner openings 42 generally corresponding to thewidth of the material to be heated, with the burners in each opposed rowbeing angled towards each other as indicated above. Thus, the system ofburners 40 illustrated in FIGS. 3 and 4 may be utilized in the apparatusschematically illustrated in FIG. 1, and in effect, replacing the burner28 of FIG. 1.

Referring now to FIGS. 5 and 6, there is illustrated an alternate typeof burner which may be employed in carrying out the process of thisinvention. More specifically, the burners illustrated comprise threeseparate burners indicated by reference numerals 46, each with agenerally circularly shaped blast opening indicated by reference numeral48, through which combustible gaseous material is discharged andignited. Each burner 46 is mounted in a staggered relationship to anadjacent burner; in effect, the pattern of burners illustrated in FIG. 4forms a pair of opposed rows of such burners (depending on the number ineach rowa factor in turn which will depend on the Width of the materialto be heated). As with respect to FIGS. 3 and 4, the burners are in astaggered relationship between the opposed rows, and are preferablyangled towards each other as will be seen from FIG. 6. To this end,again the angle is preferably between about 55 to 60.

Depending on the specific mounting arrangement of such burners withrespect to the bonding apparatus, and by adjusting the spacing of theburners to the apparatus, the effective bonding area of the flameemanating from each burner may be, as indicated by lines 50, so arrangedsuch that each burner provides a heating zone terminating at the bordersof the adjacent heating zone of an adjacent burner. In this manner, agenerally uniform temperature profile may be obtained across thecomplete width of the material being heated by such a burnerarrangement. Thus, this burner arrangement (as well as that of FIGS. 3and 4) are especially well suited for applications involving only onepair of nip rolls as shown in FIG. 6 where the nip rolls etc. correspondto that for FIG. 1.

Referring now to FIG. 7, there is illustrated one embodiment of theprocess of the present invention, in which the bonding apparatusutilizes two pairs of spaced-apart nip rolls indicated generally byreference numerals 60a and 60b; and 62a and 62b. Each roll rotates abouta central shaft 64 which may or may not be driven depending on the typeof apparatus employed. Rolls 60a and 60b are of a generally smalldiameter, which may be in the order of from about 1 inch to about 4inches, depending on their length. As will be seen from this figure,each of the rolls 60a and 60b is spaced apart from each other to 9provide a nip gap, which gap is preferably adjustable by adjustablymounting the rolls 60a and 60b by suitable means to the frame of theapparatus (not shown). With respect to rolls 62a and 62b, likewise,suitable mounting means may be employed for mounting such rolls (notshown); preferably the mounting means are such that' they permit anadjustable gap to be formed, and permit a varying degree of pressure tobe exerted on the heated material.

In the embodiment illustrated in this figure, a burner arrangement, suchas that illustrated in FIGS. 3 and 4, or in the alternative FIGS. 5 and6, may be employed and as generally indicated by reference numeral 66.The burner arrangement produces a flame indicated generally by referencenumeral 68, which is directed between the nip gap formed by the opposedrolls 60a and 60b. Between this nip gap there are fed a pair of filmwebs 70 and 72 taken from supplies 74 and 76; guide rolls 78 serve toguide the film webs 70 and 72 to the nip gap.

In this embodiment, by utilizing the arrangement shown, the spaced-apartnip rolls provide a nip gap, which in turn provides an area for the hotgases to mix and spread out, as well as level out the temperatureprofile of the flame 68. While in the present illustration, the nip gapis approximately equal to that of the flame thickness, as explainedhereinbefore, the nip gap formed between rolls 60a and 60b is preferablyof a size less than about half the thickness of the flame. This type ofarrangement has been shown to provide the best bonding strength incertain applications.

Following heating of the film materials 70 and 72 they are then broughtinto juxtaposition by nip rolls 62a and 62b, to form a bonded laminate80. This bonded laminate may then be wound up.

Referring now to FIG. 8, there is illustrated an alternate embodiment toFIG. 7. In this embodiment similar reference numerals designate similarcomponents to those described with respect to FIG. 7'but in FIG. 8, havebeen designated with a prime In'this alternate embodiment, the nip rolls60a and 60b are so mounted such that there is no nip gap formed betweenthe spaced-apart and 7 or 8, part of the products will be carriedtowards the nip along with the material to be bonded,. at1.d part willflow counter to the direction of the material. By varying the angle ofthe. burner a greater 0r..less proportion of the combustion products canbe directed away from the nip. In certain situations, for example, whereonly one of the materials to be bonded is thermoplastic, one flame maybe sufficient.

Having thus generally described suitable apparatus for carrying out theprocess of the present invention, reference will now be made to thefollowing examples illustrating preferred embodiments only.

Examples 1-6 In this series of examples, various types of thermoplasticfilm materials were bonded to various types of substrates (as describedhereinafter) using the apparatus illustrated in the drawings. Thepurpose of these examples was to produce laminates using the process ofthe present invention and to assess the bond strength and the bulktensile characteristics, of the resulting laminates produced by theprocess.

In these examples, the product designated Sample A employed high densitypolyethylene woven tape (15 x '15 tapes per square inch) fabric coatedwith low density polyethylene and which was bonded to an identicalfabric substrate. Sample B was substantially identical to Sample Awithout the low density polyethylene coating. In Sample C, orientedpolypropylene woven tape (15 x 15 tapes per square inch) fabric wasbonded to an identical fabric substrate. Sample D utilized the samepolypropylene product of Sample C, but in this case, was bonded to poundper ream (basis weight) Kraft paper.

Examples 1 to 5 were carried out utilizing the burner arrangement ofFIGS. 5 and 6, in a bonding apparatus similar to that schematicallyshown in FIG. 1. Example 6 was carried out using the burner arrangementsimilar to that of FIGS. 3 and 4, again utilizing an arrangement similarto that of FIG. 1. The following Table I indicates the processconditions and the characteristics of the resulting laminates obtained.

N0'rE.-F.p.m.=ieet per minute; p.l.i.=pounds per linear inch.

rolls, whereby the heated film material may be bonded by passing betweenrolls a and 60b-suitable pressures being applied between the rolls.

The arrangement of FIG. 2 may also be employed in combination with thatof FIG. 8 as described above, in which case the flame or flames wouldimpinge on the small 'niprolls. A single burner with two flame exits,each at an angle to the other and each directed at its corresponding niprolls, could be used to good effect in this situation. Thus, withrespect to the arrangement of FIG. 2, or the'combination of thearrangement of FIGS. 2,

This series of Examples is similar to preceding Examples l to 6, exceptthat in these examples, bonding of plain films was employed in place ofutilizing the WOV6I1 fabric substrates of the above examples. Theprocess conditions, and the product characteristics of these examples,are shown in accompanying Table II.

TABLE II 1 Process Velo- Film laminate cities, f.p.m. X10 Product-Peelstrength Number Description Bonding Flame p.l.i. (90

7 s-LDPE s-LDPE 8' gg s 3-LDPE/3-LDPE 8- 9 G-LDPE/ti-LDPE 9% :58 1o1-LDPE/1-nylon I 11 amt-nylon g; a; tags. 12 3-LDPE/1-ny n-.-. $232 =3{33%; 1a.- 1-LDPE/0.75-Mylar-. Q32 {8' 14.. 3-LDPE/0.75-Mylar 8: 2 15..lLDPE/0.5Melinex g: {8: 16.. 3-LDPE/O.5Melinex 1 11 3L 333; $3 fag-g;

0.225 20 1.3 18 2-LDPE/2Teflon(C) 19 2LDPE/2acrylic.- 202LDPTE/lpolyurethane '350 20 21..- 2-LDPE/4-vinylite 6 20 22---2-LDPE/1-polystyrene- 400 33 23 0:225 12 110-115: 24 1-LDPE/2HDPE(K)0.250 1.2. 25 3-LDPE/0.5-Al. foil g: 26 3- p 0 250 20 0 3 272-HDPE(K)/1nylon 2s... 2-HDPE(K)/O.5Mellnex. g-ggg 29... 2-HDPE(K)/paper0'250 20 30 2HDPE(K)/0.5Al. foil 0'60) 2 20 31... 2.5HDPE(V)/2.5-HDPE(V)1:000 20 32. Serlm PP/paper (tissue) 0.225 33 Paper failure. 33...1-nylon/1-nylon 0.275 3 20 4.2. 34 0.75-PP/l-cellophane 0.250 20 0.5.

1 Except as indicated in notes 2 and 3 below the roll arrangement was asshown in Fig. 6;

small roll diameter was 1.5 inches and large roll diameter was 7.8inches; pressure on large nip rolls was 126 p.l.i.; distance betweenlarge and small nip rolls was 3.875 inches; the gap 1liietween smallrolls was 46 mil; Seles Corp. SH-2 rectangular burner was used;propane-air ame.

1 Pressure on small nip rolls was 60 p.l.i. and round-tongue Selas Corp.burners (SM- 610-NA) was used.

3 Same burner as for 2 and small nip roll pressure of 5 p.l.i.

4 Indicates film failure at that peel strength.

NorE.-F.p.m.=ieet per minute; p.l.i.=pounds per linear inch; LDPE=lowdensity polyethylene; HDPE=high density polyethylene; (V)=Valeron=laminated oriented film; (K)=Koppcrs film. The number beforethe material indicates the thickness in mils oi thematerial-Mylar=polyester film; Melinex=terephthalic acid ester (Ex. 15and 16); Teilon=polytetrafluoroethylene; Viny1ite=vinyl chloride;Al.=alum1num; PP=polypropylene.

Example In this example, a round-tongue burner (SH-610-NA) was used forseaming or forming tubes of various types 7 50 invention can also beused to advantage, in the manuof film/laminates. The flame velocityemployed was approximately 19,000 f.p.m. and the bonding pressures were60 p.l.i. on the small nip rolls (as shown in the arrangement of FIG. 8)and 126 p.l.i. on the large nip rolls.

When using unoriented film, such as low density polyethylene, under theabove conditions, the bond strength (e.g. the peel strength) was at amaximum (i.e. film failure was approximately 7 p.l.i.) at a bondingvelocity of approximately 600 f.p.m.; the bonding strength then fell offfairly rapidly with increasing bonding velocity (e.g. at 1,000 f.p.m.,the peel strength was approximately 1.5 p.l.i.).

On the other hand, when using oriented film or laminates such as Valeron(the trade mark designating crosslaid, oriented high densitypolyethylene), the bond strength increased at first With increasingbonding velocity until a maximum was reached, whereafter it then fellOff. By way of example, with Valeron, the peel strength was 1.0 p.l.i.at 300 f.p.m. and approxamtely 3 p.l.i. at 800 f.p.m. At the lowervelocities the bulk properties (orientation, etc.) were affected andthose changes apparently effect the bonding of the material.

In addition to gOOd bond strength, bonding can be effected right to theedge of the film material without thin' spots developing, as it oftenthe case with conventional bonding procedures. 1 r

Example 36 In addition to the above procedures for making film-laminates, tubing, etc. it has been found that the present facture ofcap sheet bonding such as is used for block bottom bags.

Accordingly, for this example, bag ends were arranged in the form of abelt so that they came into contact with the cap sheet right at the niproll, when using an apparatus such as illustrated and described withrespect to FIG. 8. In this case, by using soft nip rolls, it was foundpossible to insure proper bonding of the cap sheet to raised outerportions only, and not any inner portion of the bag. In addition, ifdesired, to permit bonding in undesired areas, fine sprays or coats ofwater to the areas in which bonding is not desired can also be used toprevent this undesired bonding.

In one series of examples, using SH-2 burners and the arrangement ofFIG. 8, with a'fiame velocity of approximately 20,000 f.p.m. and abonding speed of f.p.m.,

with rubber covered nip rolls whichhad a durometer hardness of from 60-65, with nip pressures of 126 p.l.i. on the large nip rolls, apolyethylene peel strength of p.l.i. (including film failure) increasedto 30 p.l.i.

The above examples have been used to illustrate preferred embodiments ofthe invention; it will be obvious to those skilled in this art uponreading the teachings of this disclosure that there are many otherapplications involving the bonding of thermoplastic surfaces to afurther substrate, even though the overall operation may involveadditional steps. Thus, for example, the manufacture of certain types ofcylindrical containers (e.g. in which strips of materials are wound inan overlapping fashion around a mandrel), in such procedures where thematerials are thermoplastic, the high velocity flame teachings of thisinvention may be used to advantage to bond the strips together. Stillfurther applications of the present invention involve the use of two ormore layers of materials to be bonded or laminated together, in whichcase, the present invention may be utilized for each pair of matingsurfaces. Where the inner layers are of an open network type, such asscrim, etc., the flame or heat from the flame may readily pass throughthe network and in which case, one flame may be used to bond more thanone pair of mating surfaces. Advantageously, this may be employed in thecase where open networks (such as fibrillated film, and other scrim likematerials, or oriented high density polyethylene or polypropylene, areused to reinforce weak non-woven materials such as paper, to form adisposable reinforced fabric or laminate. In this respect, reference ismade to the teachings of copending application Ser. No. 93,646, filedNov. 30, 1970.

I claim:

1. In a method of bonding materials together wherein there is provided asupply of bondable thermoplastic material and wherein said material isheated to render the same bondable, the improvement comprising heatingthe surface of said material by applying, in direct contact therewith, ahigh velocity gaseous flame, said heating being applied to said surfaceto render said surface substantially uniformly heated in a substantiallycontinuous path thereon, said flame having a flame veloc ity of above10,000 feet per minute and a temperature of above 1,000 E, subsequentlycausing the heated surface to be brought into juxtaposition with afurther surface, and pressing said treated surface and said furthersurface to form a substantially uniformly bonded laminate.

2. A method, as defined in claim 1, wherein the flame velocity is withinthe range of from 12,000 to 40,000 feet per minute.

3. A method, as defined in claim 1, wherein the temperature is withinthe range of from about 2,000 to about 2,800" P.

4. A method, as defined in claim 1, wherein said flame is produced andincludes water vapor.

5. A method, as defined in claim 1, wherein said bonding is carried outby feeding the heated material and an additional layer of material,between a pair of opposed bonding rollers.

6. A method, as defined in claim 1, wherein there is provided at leasttwo supplies of bondable material, one of. said supplies being a web ofbondable thermoplastic material, and wherein both of said materials areheated, said method including bringing the heated materials into atleast partial juxtaposition with each other, and pressing the juxtaposedmaterials to form a bonded laminate.

7. The product of claim 9, wherein said material is bonded to itself.

8. The product of claim 9, wherein said material is bonded to at leastone further layer.

9. A bonded product, produced by the method of claim 1, and comprisingat least one layer of a thermoplastic material substantially uniformlybonded to a further layer without the use of adhesives, thethermoplastic layer having been heated with a gaseous high velocityflame having a velocity greater than 10,000 feet per minute and atemperature of higher than 1,000 E, the bonded material having theproperty of substantially no reduction in bulk characteristics comparedto the material individually forming the bonded material.

References Cited UNITED STATES PATENTS 3,210,227 10/ 1965 Shichman156--82 3,153,683 10/1964 Bryan et al. 156-82 3,481,804 12/1969 Snyder15682 ALFRED L. LEAVI'IT, Primary Examiner F. FRISENDA, AssistantExaminer US. Cl. X.R.

